A novel optical probe is used as the sensor of an automatic hydraulic model contour follower. The sensor consists of a light source, a split lightpipe, and a photodiode. With an electromechanical servo system the probe is kept at a fixed, small distance from the contour to be measured. As the servo driven probe assembly is moved across the model to be measured, output signals proportional to the horizontal and vertical displacements are fed into an X-Y plotter, thus producing a profile of the model. The accuracy is better than 1/32″ (0.80101).

Summary This paper presents an experimental study on the erosion of loose beds of sand and polystyrene by circular turbulent wall jets ol" air and water Characteristics of the scour hole have been

Automatic Device For Plotting Profiles Of Hydraulic Models

Erosion By Circular Turbulent Wall Jets

A partir des principes de calcul presentes dans la 1ere partie, presentation des resultats experimentaux des dimensions de la fosse d'affouillement, pour le dimensionnement du bassin de dissipation a prevoir au debouche de conduites de rejet en porte a faux

A comprehensive generalized study of scour at cantilevered pipe outlets. II: Results

This study has resulted in the development of criteria for the design of riprapped cantilevered pipe spillway plunge pool energy dissipators having the shape of self-formed scour holes. A literature review revealed information on the general principles of local scour at pipe exits, but inadequate practical information on scour and prevention of scour at pipe outlets. Presented herein are a research plan to provide the needed information, a description of the experimental apparatus and instrumentation, and an explanation of the experimental methods. Additional background information is a description of the scour process, and the geometry of the jet after emerging from the pipe.

A comprehensive generalized study of scour at cantilevered pipe outlets

The laboratory investigation of roughness in alluvial channels has led to the development of a special electronic device capable of mapping the streambed configuration under dynamic conditions. This electronic device employs an ultrasonic pulse-echo principle, similar to that of a fathometer, that utilizes microsecond techniques to give high accuracy in shallow depths. This instrument is known as the sonic depth sounder and was designed to cover a depth range of 0 to 4 feet with an accuracy of ± 0.5 percent. The sonic depth sounder is capable of operation at frequencies of 500, 1,000 and 2,000 kilocycles. The ultrasonic beam generated at the transducer is designed to give a minimumdiameter interrogating signal over the extended depth range. The information obtained from a sonic depth sounder is recorded on a strip-chart recorder. This permanent record allows an analysis to be made of the streambed configuration under different dynamic conditions. The model 1024 sonic depth sounder was designed principally as a research instrument to meet laboratory needs. As such, it is somewhat limited in its application as a field instrument on large streams and rivers. The principles employed in this instrument, however, have many potentials for field applications such as the indirect measurement of bed load when the bed roughness is ripples and (or) dunes, depth measurement, determination of bed configuration, and determination of depth of scour around bridge piers and abutments. For field application a modification of the present system into a battery-operated lightweight instrument designed to operate at a depth range of 0 to 30 feet is possible and desirable.. INTRODUCTION In September 1956 the U.S. Geological Survey established a research project at Colorado State University to investigate roughness in alluvial channels (Simons and Richardson, 1960). In an alluvial channel the form of the bed can be a plane, ripples, dunes, transition, standing waves, or antidunes depending on flow and sediment characteristics as illustrated in figure 1 (Simons and others, 1961). A plane bed will have surface irregularities on the order of the grain size, whereas a dune bed is composed of approximately triangularshaped elements which, in the flume, are 2 to 1G.J. Posakony, Automation Industries, Inc., Research Division, Boulder, Colo. 10 feet long and 0.2 to 1.0 foot high. A ripple bed is composed of similar triangular-shaped elements which are less than 2 feet long and are 0.02 to 0.20 foot high and may compose the major element of bed form or be superimposed on the back of dunes. Antidunes are sinusoidal undulations which, in the flume, have amplitudes from 0.05 to 0.3 foot and wavelengths from 3 to 10 feet. In the field the wavelength and amplitude of dunes and antidunes may be much greater depending on depth of flow. In the laboratory investigation it soon became apparent that measurement of the bed configuration should be made under dynamic conditions. Measurements of bed form that are made after an experiment has been concluded and the flume has been drained can be inaccurate and misleading. Because of the softness of the bed, measurements made by mechanical probing during the experiment were also inaccurate. Some method of obtaining the bed configuration, both areally and as it changed with time at a point, had to be developed. Sonic depth sounders proved the most logical type of instrument for measuring the bed configuration under dynamic conditions. However, commercial instruments, designed to operate at great depths relative to those in a laboratory flume, were not accurate enough. These commercial instruments have a minimum-depth range of about 60 feet and their accuracy is + 0.5 percent of full scale. Since the propagated sound beam in most of these instruments is a cone which has a divergence of about 20°, the beam diameter at the bottom (or bed surface) is a function of depth. The normal frequency of most commercial instruments is 50 kilocycles and their pulse repetition rate is about 500 cycles per minute. SONIC DEPTH SOUNDER FOR LABORATORY AND FIELD USE A. Typical ripple pattern, F «l ^ Weak boil E. Plane bed, F <l and d i 0.4 mm B. Dunes with ripples superposed F« I Boil-^ F. Standing waves, F > I Incipient breaking V and moving upstream11 ' C. Dunes,F <l 6. Antidunes , F > I ^^*SN^. > Breaking antidune wave t-. I*'1 * , Washed out dunes or transition, F < 1 H. Antidunes, F >l Figure 1. Forms of bed roughness in alluvial channels. In contrast, an instrument was needed which, would operate in depths of water ranging from 0.3 to 2.0 feet with an accuracy of 0.01 foot. The effective area of the bed which would reflect the sound waves should not be any greater than 1 square inch and smaller if possible; as there would be large quantities of suspended sediment, methods of minimizing its effect had to be developed; and the instrument would have to define the downstream face of the dunes which makes an angle with the horizontal of 25° to 40°. These requirements for a useful depth sounder were very stringent. The desired accuracy (small reflection area) required the use of highfrequency sound waves. However, the higher the frequency of the waves, the shorter is their wavelength. Any sediment particle in suspension with a diameter equal to or greater than the wavelength of the sound energy will readily reflect some of the sound wave. This may, in some instances, help solve other problems but in this application it was a detriment. The steep downstream face of the dune did not present a problem because the granular surface of the streambed reflected enough acoustical energy in the plane of the transducer so that an amplifiable echo was always received. In the development of the sonic depth sounder, the major accomplishments have included: 1. The design and development of transducers that have a nondiverging sound beam so as to define small changes in the streambed. 2. The development of a timing-circuit clock and a linear time-measuring circuit that can accurately (within 0.01 ft) determine the distance from the transducer face to the bed. DESCRIPTION AND SPECIFICATIONS DESCRIPTION AND SPECIFICATIONS The basic elements of the sonic depth sounder and their functions are: A. Pulser to provide timed pulses of high voltage at a given frequency. Pulses operating at three frequencies -500, 1,000,2,000 kilocycles per second -are provided. Pulse repetition rate is 400 cycles per second, the pulse duration is 1 microsecond, the pulse amplitude is 1,200 volts, and the duty cycle is 0.04 percent. B. Transducers to convert the high-voltage pulses to acoustic energy. A lithium sulfate crystal was used in the transducer to make the conversion. This same crystal is used as a receiver to detect and change the echo from acoustical to electrical energy and feed it to the receiver. Crystals are frequency-sensitive so a transducer is provided for each frequency. However, a crystal tuned for one frequency (for example, 2,000 kilocycles) can be driven by pulses of a lower frequency (500 kilocycles) but the returning echo is weaker, requiring greater amplification. The transducers are designed, using conventional acoustic theory (O'Neal, 1949; Posakony and McMasters, 1960), to maintain a nondivergent sound beam. This sound beam has very little divergence from the central axis. The area of the bed from which the sound wave is re fleeted is a function of frequency and crystal diameter. The beam diameter of the transducers used ranged from half an inch at 2,000 kilocycles per second to 1-3/4 inches at 500 kilocycles per second. To maintain a nondiverging sound beam, the size of the transducer must vary with frequency. The lower the frequency, the larger must be the transducer. The 500 kilocycle transducer is 3 inches in diameter and the 2,000 kilocycle transducer is 1 inch in diameter (Heuter and Bolt, 1955). Tomalntain anondiverging sound beam at a frequency of 60 kilocycles would require a transducer that has a diameter of about 18 inches. C. Clock to provide atime base with which the other system modules are synchronized and which the linear time circuit uses as a base to compute the time between main pulse and echo. D. Receiver to detect, shape, and amplify the small echo signals from the transducers for the linear-time-measuring circuit and display system. The receiver is provided with a variable gain so that amplification of the echo canbe controlled. This is necessary to keep interference from suspended sediment to a minimum. Excessive amplification can cause spurious echoes from the suspended sediment. The linear-time-measuring circuit measures time from the initiating pulse to the first returning echo. Spurious echoes can cause the measurement of the wrong time interval. Amplification of the signal should be set at a level at which the echo from the bed surface is sufficient to trigger the lineartime-measuring circuit. By varying the gain and frequency, it was always possible to obtain excellent definition of the bed with little or no interference from suspended sediment. E. Linear-time-measuring circuits which measure the time between the initial pulse and the echo from the bed. This time is then converted into voltage that is linearly proportional to the distance from the bed. This voltage actuates a strip-chart recorder. The linearity of the instrument is illustrated in figure 2. Here, the actual distance from the bed is compared with the strip-chart readings. F. Visual display system, consisting of an oscilloscope where the initial pulse and returning echo are displayed on the time base, for monitoring the ultrasonic information. The instrument is designed to operate at depths betweenO.2 and 4feet. Since the electronic responses of the transmitter-receiver system require a few microseconds to establish a quiescent level, the minimum depth is set at 0.2 foot. The maximum depth is limited to 4 feet to maintain the high accuracy of the linear-

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Automatic Device For Plotting Profiles Of Hydraulic Models

Citations

Erosion By Circular Turbulent Wall Jets

A comprehensive generalized study of scour at cantilevered pipe outlets. II: Results

A comprehensive generalized study of scour at cantilevered pipe outlets

References

Sonic depth sounder for laboratory and field use